Secrets of the Samurai Sword

Examine the thousand-year-old art and science behind the making of a Japanese warrior's signature weapon.
Airing October 9, 2007 at 9 pm on PBS
Aired October 9, 2007 on PBS

Program Description

(Program not available for streaming.) English archers had their longbows, Old West sheriffs had their six-guns, but Japan's samurai warriors had the most fearsome weapon of all: the razor-sharp, unsurpassed technology of the katana, or samurai sword. In this program, NOVA probes the centuries-old secrets that went into forging what many consider the perfect blade. Fifteen traditional Japanese craftsmen spent nearly six months creating the sword that NOVA follows through production, from smelting the ore to forging the steel to sharpening the blade to a keen edge capable of slicing through a row of warriors at one swoop.

Transcript

Secrets of the Samurai Sword

PBS Airdate: October 9, 2007

NARRATOR: The samurai were the heroes of ancient Japan.
Still, today, their legend continues. The samurai's sword is one of the
greatest fighting weapons of all time, perfectly engineered for close-up
combat, renowned for its deadly cutting edge.

Modern
science can now reveal the technical excellence of this ancient craft.

MICHAEL
NOTIS (Materials Scientist, Lehigh
University): It's
certainly an object of absolute beauty, from both an aesthetic and a scientific
point of view.

NARRATOR: But can it explain the mystery of how these
swords were made?

STEPHEN
TURNBULL (University of Leeds): The great swordsmiths of Japan were steeped in the
mysterious traditions of the metal. They were able to transform this mystery
into something that was very, very real: the samurai sword.

NARRATOR: It is said that the sword is the soul of the
samurai. Can modern science uncover its secrets? Coming up on NOVA, the Secrets
of the Samurai Sword.

NARRATOR: By day, Midori Tanaka is just another face in the
crowd on the busy streets of modern Japan, working as a mild-mannered
receptionist for a midsized electronics company. By night, however, she is
anything but mild mannered.

Midori
is an expert swordswoman, descendent of a long line of samurai warriors.

The
samurai were noble warriors of medieval Japan, similar to the knights and
noblemen of Europe. During this
600-year era, beginning in the 12th century, Japan was ruled by regional
warlords. The samurai were part army, part aristocracy, and, at times,
freelance mercenaries. They lived by a strict code of honor that demanded rigid
discipline and unfailing loyalty. Their sword is one of the greatest fighting
weapons of its day, if not of all time. It could cut a man in half with a
single stroke.

Today's
swordsmen and -women test their mettle on bamboo and rolled straw: not easy to
cut with just any knife, and similar, it is said, to the toughness of cutting
through human bone. The sharpness and strength of the sword is legendary.

Legends
are one thing, but how does the quality of the samurai sword stand up to the
test of time?

Mike
Notis, a samurai sword expert, is a professor at Lehigh University, a leading
materials engineering school that has an important history with the once-great
American steel industry.

MICHAEL
NOTIS: If you look at the blade
itself and you look at the surface appearance, you see one level of beauty. But
with the instruments that we have available, we can go to different structural
levels, and we can see the care and the fabrication capability that these
craftsmen had to make an object of absolute beauty, from both an aesthetic and
a scientific point of view.

NARRATOR: This remarkable weapon reveals a highly developed
metal-making skill that dates back more than a thousand years, to 900 A.D. The
electron microscope can now reveal the quality of this ancient steel, as well
as some of the secrets of its skillful engineering.

MICHAEL
NOTIS: And this is the boundary.

NARRATOR: Embedded deep into the material of the blade are
different types of steel, each contributing to the sword's deadly
effectiveness and its unique design.

MICHAEL
NOTIS: There are two types of blade
weaponry. One is a piercing instrument, an epee, or a fencing foil, for
example. The other is the saber or the Japanese sword, where you slash. You use
your whole body force, your upper body, in order to apply the largest force you
can. The unique aspect of the Japanese sword is that the craftsmen were able to
put the right materials in the right place to get optimum properties for the
entire object.

NARRATOR: In our common understanding, we think of all
metals as strong. But in fact strong metals have other important
characteristics. Controlling these characteristics requires expert formulation.
So how, in the absence of understanding this science, were the ancient
craftsmen of Japan able to achieve such technical excellence?

In
the small village of Shimane, in southwest Japan, they still make the metal ore
for samurai swords the same way it has been done for centuries, in earthen
smelting furnaces called tataras.

Akira
Kihara is one of the last remaining tatara masters in the world. He won't
sleep for three days and three nights as he watches the furnace create steel
that is the quality needed for the world's sharpest swords.

This
special steel called tamahagane is made from iron ore sand, collected in local rivers,
and charcoal.

AKIRA KIHARA (Tatara Master): Within an hour, the iron sand sinks to the bottom,
to what we call the bed of fire. When we look at the bed of fire we can clearly
see, from the color, whether or not it has become tamahagane.

NARRATOR: The traditional Japanese smelting furnace is
constructed out of clay with a row of inlets along the sides. Air is blown into
the furnace with bellows that drive the temperature up to nearly 2,500 degrees
Fahrenheit. Think of this as a very hot oven, because at this stage, making
steel is a lot like cooking.

RICHARD P.
VINCI (Materials Scientist, Lehigh
University): Steel is basically
iron, and to that you add a little bit of carbon, and the carbon gives it much
more strength than the iron would have by itself.

NARRATOR: Rick Vinci, a professor of material science at
Lehigh University, says that just like in cooking, the ingredients of the metal
can make all the difference.

RICHARD
VINCI: It is a little bit like
being in the kitchen and adjusting a recipe by adding a pinch of salt, or maybe
you say, "Oh, boy, this could really use just a hint of lemon," and
somehow that little bit really changes the food. In the same way, some of these
subtle chemistry changes can really make important adjustments to the overall
properties of the metal.

NARRATOR: By the end of the second day, the furnace has
already eaten up 18 tons of iron ore, sand and charcoal—the fire's
fuel and also the source of its carbon.

MICHAEL
NOTIS: Steel is composed of the
element iron and the element carbon. The ancient Japanese could physically see
iron, but they had no idea what carbon was. They understood that charcoal was
needed for the process, but they didn't understand charcoal as carbon.
Carbon wasn't discovered as an element until just a few hundred years
ago.

NARRATOR: Today the recipe is no secret. The hard part is
keeping the oven cooking just right. Throughout this smelting process, Kihara
must tend to the furnace to make sure that nothing goes wrong.

AKIRA
KIHARA: The furnace is
like a human being. We can think of the iron and coal as food we feed her. She
digests it so that she will bear good tamahagane.

NARRATOR: Inside the furnace, the iron and carbon are
slowly forming into the right mixture. Beneath the furnace, lies a chamber
nearly 10 feet deep. Ventilation channels flank either side. Any moisture
seeping in from the ground would lower the temperature, ruining the steel, and
they would have to start all over again.

In
the very hot center of the furnace, the iron and carbon combine. This process
happens at the atomic level. By nature, iron atoms bond to one another in a
specific geometric arrangement. When heated, that structure changes form.

RICHARD
VINCI: Iron actually has two
different forms that it takes: a low temperature form, in which the atoms are
arranged in a particular way, and a high temperature form, in which they are
arranged a little bit differently. There's actually more space between
the iron atoms at high temperature.

NARRATOR: But when this high temperature form cools
quickly, it contracts, and the carbon atoms become trapped in between the iron
atoms.

RICHARD
VINCI: If it does that, the
iron can't fully assume the structure that it would like to. It will be
distorted by virtue of the fact that the carbon atoms are lodged into these
spaces that are really too small for them to fit into. And that kind of form of
steel—iron and carbon mixed together—is very, very hard, very, very
strong.

NARRATOR: Manipulating this heating and cooling process, as
well as controlling the ingredients in the steel, allows metallurgists or
ancient craftsmen to change the properties of the metal.

RICHARD
VINCI: Metals are elements, so
they are made up from single kinds of atoms. Most of the elements on the
periodic table, it turns out, actually are metals, even though we don't think of them as metals. We usually
think of metals as being solids; they are shiny, they conduct electricity and
heat really well. And perhaps more importantly for a lot of their uses, they
have this ability to bend, to take on new forms and also to have their
mechanical properties be controllable. And so by adjusting their chemistry and
adding a little bit to them or taking something away, by controlling their heat
treatment, you have a lot of control over their properties, and this makes them
very, very versatile and, really, the underpinnings for the modern society that
we live in.

NARRATOR: Modern like the skyscrapers on the busy streets
of Japan. These towers of steel have their roots in the ancient metal-craft of
the sword.

In
the traditional smelting process, the metal ore never completely reaches a
liquid state so that the steel ore, or tamahagane, will not be uniform in its
mixture of iron and carbon. Some parts will have more carbon, some less. These
different mixtures of steel will become very important in the engineering of
the sword.

More
carbon makes the steel harder so that it can hold a sharper edge, but too much
carbon makes the steel brittle, and no samurai wants to be caught with a broken
sword.

In
engineering, there is a limit to how hard you can make the metal before it
becomes brittle. The standard test for measuring this is called the Charpy
test. Here, a large pendulum is used to break a sample of metal. Hard metals don't
bend, so they break more easily. A metal that resists the energy or force of
the pendulum and bends before it breaks is said to be tough.

RICHARD
VINCI: In the case of tough
metal, instead of just breaking, it actually bends. And, so, what you'll
see is a lot of stretching on one side of the metal until, eventually,
it's been torn apart. It actually looks a fair amount like if you take a
piece of taffy or a Tootsie Roll—and as you know the Tootsie Roll or the
taffy will stretch first and then it will come apart—and you will see the
effect of that stretching. You want very large energy absorption to have a
tough metal. You want it to be able to take a lot of damage before it breaks.

NARRATOR: At Lehigh University, these basic principles of
toughness and hardness are put to the test, literally. The ATLSS Center is one
of the largest metal testing facilities in the United States. Here they can
test huge metal structures to see how they will stand up in the real world.

RICHARD
VINCI: Every time a building
is built, all of the steel that goes into that building must be qualified
before it can be used in the structure. And some of those tests include
hardness and toughness measurements.

NARRATOR: Steel beams from skyscrapers and bridges are
trucked here to be put through punishing tests that simulate major earthquakes
or a hundred years of heavy truck traffic.

ALAN W.
PENSE: It is quite a bit of
motion, though. I don't know, getting a structure to survive with that
kind of motion is, I think, very, very impressive.

RICHARD
SAUSE: Collapse prevention: that is what
we are after.

ALAN W.
PENSE: Collapse prevention,
right. See how it's deforming and bending but not cracking?

NARRATOR: The test is recorded in time-lapse footage that
shows these structures pushed to the breaking point. Engineering metals,
whether in a sword or on a super highway, is about making sure they are tough
enough to last.

ALAN W.
PENSE: And this whole test
took how long?

RICHARD
SAUSE: This test took a whole day. It
simulates 30 seconds of earthquake.

NARRATOR: At the back of the ATLSS center is an area they
call the graveyard. Here is the final resting place of structures that
weren't tough enough to stand the test of time.

Working
with metals has always been dangerous. Back at the smelting furnace, there is a
Shinto shrine devoted to a sacred deity the workers believe helps keep them
safe. These elaborate rituals are not just about safety, but, as Mike Notis
explains, they are also about quality control.

MICHAEL
NOTIS: In modern industry, today, we
depend very strongly on quality control. The ancient Japanese swordsmiths used
religious ritual as their process control to make sure that each and every time
that they manufactured this same object, it was done exactly the same way. They
didn't have science to do it, they had religious ritual.

KENNETH
KRAFT (Buddhist Studies, Lehigh
University): If you think that
what you are doing has religious significance, you pay extra attention to it.

NARRATOR: Ken Kraft, a professor of religion and an expert
on medieval Japan, says this reverence helps explain why the sword is so
important in Japanese culture.

KENNETH
KRAFT: They'd say that the sword is
the soul of the samurai. In almost all pre-modern cultures, matter and spirit
were interfused, and so it wasn't so hard from theâ¦to imagine that
an object could have this kind of power—what's called the luminous
power or an otherworldly power. And in Japan, the gods could be found in any
natural object, including waterfalls or trees or a mountain. So it wasn't
a big leap for them to think that an object as powerful and as beautifully made
and as reverently made as a sword could have some sacredness to it.

NARRATOR: It is that sense of the sacred that drives Master
Kihara. After 36 hours of feeding the voracious fire, everyone is exhausted,
but Kihara carries on, never sleeping, always keeping vigil.

In
ancient Japan, sword makers and the weapons they helped to produce were vital
to the noblemen and the samurai. They were the military-industrial complex of
their day, which helps explain why their metal techniques became so advanced.

KENNETH
KRAFT: Around the whole world, in 1700,
the Japanese were the masters of this particular technology that produced
swords. So we have to remember we're dealing with a culture in which the
military dominated for 4- or 500 years. That gave them a lot of time to perfect
whatever military implements they wanted.

NARRATOR: Using only the ancient methods, Kihara monitors
the process by watching and listening to the fire. On the morning of the fourth
day Kihara can tell by looking and listening inside the core of the tatara that
it is time to break up the furnace and extract the steel ore.

AKIRA
KIHARA: I could see the
core. It looks good. That's a big relief. I'm happy.

NARRATOR: Happy, yes, but no one can afford to relax yet.
Until they get the steel out, there's no way of knowing if it's
samurai-sword grade or only good enough for kitchen knives.

Once
the ingot is cooled, it will be broken into small pieces. This process helps to
sort the steel. Pieces that break off easily are more brittle. Parts that are
more difficult to break apart are tougher. The most skilled masters are those
that can deliver the best quality of both types.

AKIRA
KIHARA: It's like
when your child is born, it was worth waiting for. I am very happy.

NARRATOR: Kihara will then choose which of these pieces is
good enough to go to the sword maker, who will give this raw steel its famous
shape.

While
craftsmen like these keep the tradition of sword-making alive, the legend of
the samurai also lives on in the popular imagination. The samurai are to the
Japanese culture what cowboys are to America, heroes of a lost era.
Surprisingly, samurai movies had a big impact on the American Western itself.

Akira
Kurosawa's famous film, Seven Samurai
was turned into the classic western The
Magnificent Seven. The stories are nearly identical. Seven brave
warriors rescue a poor village from bandits. The heroes are reluctant to use
their weapons, but expert at it. Both of the leading men are bald: Takashi
Shimura and, famously, Yul Brynner. There is one big difference: in the
American version, the sword was replaced by the classic six-shooter. Both,
however, do the trick.

VOICEOVER (A Fistful of Dollars): The man with no name. Danger fits him like a tight
black glove.

NARRATOR: Another Japanese classic, Yojimbo,
became A Fistful of Dollars
which launched Clint Eastwood's movie career. Even Tom Cruise tried his
hand, as the improbable Last Samurai.

All
of these movies show that sword fighting, like the gun battles in westerns,
makes for good cinematic action. One samurai film buff calls it "sword
porn." To create the perfect fighting sword, or prop, form and function
were engineered together. The laws of physics dictate the sword's unique
curved shape.

RICHARD
VINCI: With the curve of the
blade, if you are doing that slashing motion, it actually makes it possible to
move the blade in an arc, which is what you want to do when you slash
something. If you have a straight blade and you attempt to slash, at some point
you have to slash and then pull, because the blade is straight.

NARRATOR: To create its unique shape, the raw steel must be
forged into the fighting blade. And while the work of a blacksmith seems pretty
straightforward—brute strength that muscles metal into shape—the
real secret is what is going on deep inside the metal.

Sakurai
is a small town, not far from the fabled city of Kyoto and home to Gassan
Sadatoshi, one of Japan's most renowned swordsmiths. His family has been
in the business for generations.

The
pieces of raw steel arrive from the smelters. Together with his son and
assistant, Gassan carefully examines the tamahagane to see if it is up to
scratch for his next sword.

Gassan can judge from the texture and color of
the raw steel just how much carbon is in it. Brighter pieces have more carbon.

STEPHEN
TURNBULL: The great swordsmiths of Japan
were far more than just blacksmiths. They weren't just people who bashed
metal into a sword shape, they were more like alchemists.

NARRATOR: Historian Stephen Turnbull, from the University
of Leeds, is a renowned expert on the samurai sword.

STEPHEN
TURNBULL: They were steeped in the
mysterious traditions of the metal: how it was melted, how it was molded, how
it was beaten. They may not have understood the chemical composition of it, but
from years of practice, years of apprenticeship, and years of tradition, passed
on from master to pupil, they were able to transform this mystery into
something that was very, very real, the samurai sword.

NARRATOR: Remember how, at the smelter's furnace,
some of the metal was of a different atomic composition that made it either
harder or tougher? Gassan needs to find the best quality pieces of both types,
because part of his art is to find a way to combine them so that the sword will
have the advantages of their different characteristics.

There
is really still only one way to learn the art of sword making, through
apprenticeship—no easy career path. They rise at dawn, help with
household chores, and work with their master six days a week. It takes years to
learn correct forging technique.

The
untreated metal is protected from rusting before the process begins. Heating
softens the steel for hammering so that the pieces can be formed into one. The
hammering also drives out most of the remaining impurities, called slag. Molten
slag can be seen in some of the dramatic sparks as it is squeezed out of the
steel by the hammering.

The
steel is pounded flat and then folded time and time again to thoroughly mix the
iron and carbon. Gassan gauges the concentration of the carbon by the way the
steel bends.

How
good a job did the ancient blacksmiths do? With modern tools we can see. Using
a special electron microscope, trace amounts of unwanted elements like sulphur
or phosphorus that would weaken the steel can be detected.

MICHAEL
NOTIS: And what you see on the right
side is the x-ray spectra collected from that area, which shows only the
presence of iron, which is the high peak, and carbon all the way to the left,
which is the low peak. We can tell this is a very high quality steel.
It's got only iron and carbon present in it.

NARRATOR: Another thing that is happening in this brutal
pounding of the steel is that the shape of the metal, all the way down to the
atomic level, is changing.

RICHARD
VINCI: The material is
actually getting harder as it's hammered. Many people have the experience
of bending something and feeling it get harder. A great example is if
you're trying to run copper tubing, installing an icemaker or doing
something like that.

Initially,
when you get the tube in a coil, like this, it's relatively easy to
change its shape. You can straighten it, make it go around corners, whatever
you like to do. But if I make a mistake and try to change the shape of it at
this point, once it's already been straightened, it gets much more
difficult the second time, and even more difficult the third time, to
straighten it out again. Because every time I bend it, I create lots of
microscopic defects inside, and the more defects I have, the stronger the
material gets.

Now,
the smith, ultimately, would like to keep changing the shape of the sword, and
so this hardening is not really what he wants. So he can put that sword back in
the flame, heat it up, and the heat will heal the defects. At that point the
material will go back to being relatively soft and formable, and the cycle can
be repeated over and over again.

NARRATOR: These defects also play a key role in giving
metals one of their unique characteristics, their bendability. As Vinci
explains, this bending happens at the atomic level.

RICHARD
VINCI: Metals have this
capability in which, when you apply a stress, the atoms can move, and they can
swap locations within their general arrangement. They don't mind being in
this position or this position or this position. And for that matter, when they
move from one position to another, they really don't mind temporarily
being in between. Now in many of the other hard materials, for instance
ceramic—like your typical coffee mug—that might be made up of two
different kinds of atoms, and they are arranged in a very specific way. They
don't want to switch positions at all. If you apply stress to it, the
atoms will start to move, and there will be greater and greater resistance to
that movement until, ultimately, it's actually easier for the material to
fracture than to change shape. And so if you drop a metal mug, it will
typically land, and it may dent, but if you drop a ceramic mug, it really
doesn't have the ability to dent, and instead it cracks, and you end up
with a broken mug.

NARRATOR: The art of sword fighting also requires its own
kind of hardening by fire. Midori studies sword fighting technique three nights
a week under the watchful eye of her father, Fumon Tanaka.

Tanaka
is a grand master swordsman and believes that the samurais' code of honor
and their values, called "Bushido," are important to maintain.

FUMON TANAKA (Samurai Grand Master): I think many Japanese people can still find the
spirit of the Samurai in their hearts. We have started to judge everything with
money, or if you own a big house, or drive a nice car. But the spirit of the
warrior was different. Honor was more important; to give your best at all times
was important. This is the spirit of Bushido that we should not forget.

NARRATOR: Midori started training when she was a small
child, and her father hopes that she, too, will be a grand master.

MIDORI
TANAKA: It is a lot of responsibility. I
cannot let the tradition die out with my generation. So I practice everything I
learn very hard.

NARRATOR: By any standard, Midori and her father have an
unusual relationship, and an odd way of demonstrating their mutual respect. In
this ancient test, Midori will shoot an arrow at her father's heart. He
has only his sword to defend him.

The
arrow can penetrate a board over one centimeter thick, more than enough to kill
a man and to make a young
student a little nervous.

Light,
perfectly balanced and hard enough to cut through armor, in the hands of a
fully trained samurai, the sword is the ultimate weapon for close combat. But
can the sword save him from a speeding arrow?

It's
not only Master Tanaka's ability to react in the face of a speeding
arrow, but also the sharpness of his sword that allows him to sever it
mid-flight and defend himself from his daughter's pointed barbs.

The samurai needs a sword that is both hard and
flexible, but remember that there is a tradeoff. Hard metals, with more carbon,
hold an edge but are brittle and can break. Tough metals bend, but can't
hold an edge. Smelting creates pieces of both types which are then purified and
shaped.

Now
is the crucial moment when both types of steel are forged together. The hard
steel is pounded flat and then folded into a u-shape. The tougher low-carbon
steel is heated to a glowing red and inserted into the core. This relatively
simple procedure is the culmination of a great deal of work and key to the
ultimate success of the sword.

Now
the metal the samurai needs is where it is most needed. The hard steel is
wrapped around the outside to allow for the cutting edge to be razor sharp, and
at the core, where the sword needs to absorb the impact of those deadly blows
and be more flexible, Gassan uses the tougher steel.

RICHARD
VINCI: The sword is an
excellent example of people, first of all, understanding the requirements of
the particular application, and then the ability to understand how to achieve
those properties through the right choice of materials and through the right
processing. So it's an excellent analogy for what people do when they
build a complicated, modern, engineered structure.

NARRATOR: The success of the ancient swords'
engineering was judged by a rating system that was as ghoulish as it was
efficient. Sword testing and the criminal justice system of ancient Japan went
hand in hand, so to speak. Depending on the severity of someone's crime,
they could have an appendage chopped off. Stealing might lead to the loss of a
hand; bigger crimes had more severe penalties.

RICHARD
VINCI: By modern standards,
testing a sword using actual body parts is, of course, really distasteful. But
from a practical point of view, very effective, because that is really what the
blade is designed to do.

MICHAEL
NOTIS: A blade that would go through
a body at its midsection was certified as a better blade than would go through,
for example, somebody's wrist, or ankle. A blade that could go through
two bodies, or three bodies, or four bodies, or even five bodies, as some
inscriptions read, was believed to be the best blade. And those that are in
existence today are in the best Japanese museums that you can find; a
"five-body" blade.

NARRATOR: A "five-body" blade—think of it
as a kind of grotesque Good Housekeeping Seal of Approval.

At
Gassan's forge, a much more delicate work is underway. The final stage of
the forging process will harden the steel to hold its razor sharp edge. It is
done through a dramatic step of heating and quickly cooling the steel to lock
in the carbon. This process, called quenching, will accentuate the hardness of
the high-carbon steel but has little affect on the tough, more flexible,
low-carbon steel.

RICHARD
VINCI: Now I'm going to
show you what happens when you heat and then quench a piece of low-carbon
steel, similar to that that you'll find inside the core of the sword. In
its initial form it bends, really, quite easily. Now I'm going to
simulate the heating and quenching sequence that a smith would put the steel
through, using a blowtorch. I'm going to heat the end of the steel rod
here to the point where it's orange-hot, so the carbon has gone into
solution. And, once the end is nice and hot, I'm going to plunge it into
some cool water, very, very rapidly cooling it. And it retains most of its
bendability.

Now,
let's take look at the very-high-carbon steel. It's like the
cutting edge of the sword. When it comes out of the box, just like the mild
steel, I can bend it very easily. Let's see what affect this had with the
high-carbon steel: very brittle, very easily broken. The material is very hard,
but not very tough. If you had an entire sword made out of a material this
hard, it would be very likely to shatter on the battlefield.

You
could make a glass sword that would have a wonderfully sharp edge and might
actually cut something one time, but very rapidly you'd see the
shortcomings of following that kind of approach. You'd be emphasizing
only hardness at the expense of other important properties, like toughness.

NARRATOR: Gassan prepares the sword for the dramatic
quenching stage by painting on a secret mixture of clay and charcoal powder.
This will insulate parts of the blade allowing some parts to cool even more
quickly than other parts. In time, it will also reveal one of the most unique
signatures of the samurai sword.

The
sword is now ready for this crucial moment. Gassan darkens the forge so that he
can judge, by the color of the metal, exactly when the sword edge has reached
1,500 degrees Fahrenheit. Too hot and the steel might crack, too cold and the
quenching would fail.

MICHAEL
NOTIS: The most critical time in the
whole sequence is this quenching operation. As many as one out of three blades
is lost at this point in time.

NARRATOR: Gassan is ready to pull the sword at a
moment's notice.

RICHARD
VINCI: When the smith plunges
it into water, the two different parts of the sword are both contracting. The
part with low carbon—this is the part inside the core of the
blade—is able to contract pretty much like it would like to, because
there's really not much carbon in there to be trapped. So it shrinks a
lot. The part on the outer surface though, is filled with carbon, and so
it's really prevented from shrinking as much as it would like to.

So,
if you can imagine this part being the core of the blade and this part being
the edge, the top part is going to shrink a lot more than the bottom part and
when it does so, it automatically builds a curvature into the blade.

NARRATOR: The two types of steel contracting at different
rates forces the blade to curve, giving the samurai sword its distinctive,
body-hugging shape.

Risuke
Otake is one of the world's finest martial arts experts. At 80 years old,
he is still driven to pass on the way of the Samurai and teach how to use the
unique curved sword to its best advantage.

RISUKE
OTAKE: You should attack
here and here, at the arteries and at the heart. If you cut from the other side
you won't reach them. So attack here or attack the neck.

When
you fight, you should never have the sun in your face, you should always keep
the sun or the moon behind you. You can use it to blind your enemy. The best
warrior is one who can turn circumstances to his advantage in a fight.

NARRATOR: To study with the master, every student takes a
blood oath to uphold the true spirit of the samurai code. Only the most
advanced students are allowed to trade in their fighting sticks for sharpened
swords.

The
final stage of this thousand-year-old craft will give the sword its legendary
fighting edge. It will also make or break the value of the sword.

Master
Takeshi Hon'ami is a 14th generation sword polisher. He will spend
several weeks bringing the forged steel to a brilliant luster. It takes a
lifetime to master this trade. Even learning how to sit isn't easy.

Hon'ami's
polishing stones are rare and can cost a thousand dollars or more. After 10
days of polishing, he moves on to one of the finest stones, the jizuya, so
small it is sometimes no bigger than a grain of rice.

Although
he keeps the edge of the katana, or sword, turned away from his body, it takes
extreme concentration to rub these stones against some of the sharpest steel in
the world.

TAKESHI
HON'AMI (Sword Polisher): Katanas are very sharp. When I was younger I used
to cut myself a lot. Even these days, I'm still very nervous.

NARRATOR: It is only through his intensive polishing that
the full beauty of the sword is achieved and a hidden beauty is revealed. Just
before quenching, clay was painted onto the blade. Only now can the full effect
of this be seen. Embedded in the steel is a visible line called the hamon. This
wavy line is considered a great art form and is created by the skillful
manipulation of the steel's inner structure.

RICHARD
VINCI: What you will see in a
macroscopic level is a difference in color or brightness on those two regions.
What you're really seeing is a macroscopic effect that comes from the
different arrangements at the atomic level in those two regions of the metal.

GASSAN
SADATOSHI (Swordsmith): The creation of this line doesn't just show
the skill of the swordsmith, it's also an expression of his creativity,
and it gives every sword a unique character.

NARRATOR: The cutting edge is, of course, what the samurai
sword is all about, and honing the sword's sharp tip is the last step in
the process.

TAKESHI
HON'AMI: We say making the tip is
like applying makeup on your face, because the tip of the sword is what you
show to the world.

NARRATOR: Beauty is in the eye of the beholder, whether
that is expert swordsmanship, fast paced cinematic swordplay, or simply the
quality of the sword metal itself.

For
Midori and her father, the beauty of the sword is that it symbolizes important
values from the past. Learning to use the sword is their way of keeping these
traditions alive for future generations.

In
modern Japan, there is a struggle between maintaining these traditions and
embracing contemporary values. The lore of the samurai remains one of the key
links to that past. Long after the gun had replaced swords as a weapon,
Japanese soldiers in World War II still carried their swords into battle,
although many were mass produced in the quickly industrializing war economy.
Even today, when Japan's battles are economic not military, the reverence
for the sword endures.

It
has taken 15 people nearly six months to make this one sword. Blacksmith
Gassan, finally, can now see the results.

GASSAN
SADATOSHI: A sword that I spent so much
time on, to see it finished, with all its characteristics brought fully to
light, it leaves me speechless.

NARRATOR: Now finished, it is perhaps appropriate that even
though the sword will never be used for its original purpose, thankfully, it
has not lost any of its value in Japanese culture. Exceptional samurai swords
can sell for hundreds of thousands of dollars as art objects and antiques.

So,
today, the samurai sword has moved from the bloody battlefields to the
rarefied—some would say cutthroat—world of art collectors, perhaps
another sign of the legendary resilience that was engineered into the sword
more than 1,000 years ago.

Sources

Links

Naginata Blade Constructionwww.scnf.org/forge.htmlRead about the forging, tempering, and polishing of the samurai sword at this Web site from the Southern California Naginata Federation.

steeluniversity.orgwww.steeluniversity.orgConduct your own virtual Charpy test and learn more about modern steel production at this award-winning Web site from the International Iron and Steel Institute.

Lehigh University Institute for Metal Formingwww.lehigh.edu/~inimf/Lehigh University, one of the foremost schools that studies metals, offers information on current metals research on its Web site.

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Major funding for NOVA is provided by the David H. Koch Fund for Science, the Corporation for Public Broadcasting, and PBS viewers.